The present invention relates generally to the field of substrate processing equipment. More particularly, the present invention relates to a method and apparatus for detecting wafer centering during operation of a semiconductor processing apparatus. Merely by way of example, the method and apparatus of the present invention have been applied to the use of an optical emitter and emitter mounted on a translatable stage to determine wafer position during wafer rotation in a process chamber of a track lithography tool. The method and apparatus can be applied to other processing devices for semiconductor processing equipment utilized in other processing chambers.
Modern integrated circuits contain millions of individual elements that are formed by patterning the materials, such as silicon, metal and dielectric layers, that make up the integrated circuit to sizes that are small fractions of a micrometer. The technique used throughout the industry for forming such patterns is photolithography. A typical photolithography process sequence generally includes depositing one or more uniform photoresist (resist) layers on the surface of a substrate, drying and curing the deposited layers, patterning the substrate by exposing the photoresist layer to radiation that is suitable for modifying the exposed layer and then developing the patterned photoresist layer.
It is common in the semiconductor industry for many of the steps associated with the photolithography process to be performed in a multi-chamber processing system (e.g., a cluster tool) that has the capability to sequentially process semiconductor wafers in a controlled manner. One example of a cluster tool that is used to deposit (i.e., coat) and develop a photoresist material is commonly referred to as a track lithography tool.
Track lithography tools typically include a mainframe that houses multiple chambers (which are sometimes referred to herein as stations) dedicated to performing the various tasks associated with pre- and post-lithography processing. There are typically both wet and dry processing chambers within track lithography tools. Wet chambers include coat and/or develop bowls, while dry chambers include thermal control units that house bake and/or chill plates. Track lithography tools also frequently include one or more pod/cassette mounting devices, such as an industry standard FOUP (front opening unified pod), to receive substrates from and return substrates to the clean room, multiple substrate transfer robots to transfer substrates between the various stations of the track tool and an interface that allows the tool to be operatively coupled to a lithography exposure tool in order to transfer substrates into the exposure tool and to receive substrates after they have been processed within the exposure tool.
Over the years there has been a strong push within the semiconductor industry to shrink the size of semiconductor devices. The reduced feature sizes have caused the industry's tolerance to process variability to shrink, which in turn, has resulted in semiconductor manufacturing specifications having more stringent requirements for process uniformity and repeatability. An important factor in minimizing process variability during track lithography processing sequences is to ensure that substrate or wafer is properly centered during the performance of processing steps. During semiconductor device processing, it is preferable to accurately center the wafer on a support platform or chuck in order to ensure the wafer will receive uniform processing across its entire process surface (e.g., uniform photoresist layers during photoresist spin processes). In addition, for processes sensitive to crystal orientation or pattern alignment, wafers are generally provided with a notch or flat to signify the substrate's crystal orientation or pattern alignment. During processing steps, alignment of the wafer using the notch or flat is performed to place the notch or flat in the appropriate location with respect to the chamber components.
Wafer centering devices exist in which an optical emitter and an optical detector are placed on opposite sides of the wafer and light passing around the outer edge of the wafer is measured at the optical detector. The accuracy with which the wafer is centered on the chuck is then determined. However, in some track lithography tool applications, such wafer centering designs are not practical due to the use of fluids such as photoresist, which can result in unwanted contact between the optical elements and the processing fluids.
Thus, there is a need in the art for improved methods and systems for detecting wafer centering during track lithography tool operations.